Nowadays, the use is known of spindles that self-expand on mechanical command which are installed on one end of each moveable arm comprised in unwinders adapted to support and rotate spools of paper, cardboard, corrugated cardboard and flexible laminates in general, in order to enable the processing thereof in the production process.
The operation of these conventional self-expanding spindles, which as mentioned operate on mechanical command, involves the radial expansion of blocks actuated by a supporting pin which is eccentric in shape and is integral with the bearing transmission shaft of the unwinder with movable arms.
Such blocks exit automatically from the self-expanding spindles upon the rotation by a fraction of a turn of the supporting shaft of the unwinder, and they make it possible to retain and center a spool, and also to support its weight during rotation.
This principle of operation of conventional self-expanding spindles has the advantage of exerting a high radial force for clamping the spool, since the blocks take advantage of the eccentricity of the supporting pin. In particular, this radial force is exerted on the internal part of the spool, called the “core”, around which the paper or the like is wound and which is made of very robust material.
However, such conventional self-expanding spindles have the drawback that this clamping is substantially irreversible, so that the core of the spool remains coupled to at least one self-expanding spindle during the operations to unload the spool, thus necessitating difficult manual interventions by the operators for its removal, which very often cause consequent damage to the core.
Note that the cores of the spools must necessarily be recovered undamaged in order to enable their subsequent reuse, and therefore their damage implies a considerable economic burden that negatively influences production management.
Furthermore, the manual interventions in order to free the cores of the spools are typically carried out by way of levers and in restricted spaces, with consequent operational hazards and risk of injury for the operators.
Another drawback of the conventional self-expanding spindles consists in that they do not offer the possibility to unload spools that are not completely used, which need to be recovered in order to be reused in subsequent processing cycles, at the center of the unwinding station and in conditions of safety.
These partially used spools have masses in the order of hundreds of kilograms and when, during the unloading operations, they remain coupled to at least one self-expanding spindle, their expulsion and their movement is very difficult and problematic.
The situation described up to this point has led the producers of unwinders with movable arms to provide servomechanisms to be placed at the rear of the self-expanding spindles, so as to automatically perform the operations of expulsion and unloading of the spools, for example by way of a remote command and without the presence of operators in the area of the unwinding station, so as to avoid downtimes, risk of injury and, more generally, to remedy the above mentioned drawbacks.
Since conventional self-expanding spindles are typically flanged to the supporting shaft of the unwinder with movable aims, these servomechanisms comprise at least one annular pusher, fitted between the self-expanding spindle and a moveable arm, in particular being fixed on the moveable arm so as to be able to exert a pushing force originating from the rear side of the self-expanding spindle.
Currently, the solutions in use comprise an annular cylinder, inside which an annular piston slides which is moved by compressed air that provides a pushing force proportional to its area and which performs half of the necessary stroke for the expulsion of the spools from the self-expanding spindles.
Once the halfway point of the stroke is reached, the annular piston places under pressure a series of smaller, auxiliary pistons of reduced diameter or cross-section.
The movement di these auxiliary pistons makes it possible to perform the full stroke necessary for the expulsion of the spools from the self-expanding spindles, unloading them at the center of the area of the unwinding station.
However, such conventional solutions are not devoid of operational and economic drawbacks, among which is the fact that the pushing force, exerted on the spool for its expulsion from the self-expanding spindles, is determined by the diameter, i.e. by the cross-section, of the auxiliary pistons, and so in practice the pushing force is of reduced value, and therefore is not adapted to the expulsion of spools of considerable mass.
Another drawback of such conventional solutions consists in that they have large diameters due to the complexity of their construction, which entail a consequent limitation of the useful spaces available for the angular movements of the moving arms of the unwinders.
A further drawback of such conventional solutions consists in that they have large longitudinal dimensions due to the complexity of their construction, which entail a consequent limitation of the useful spaces available for the rotation and movement (loading and unloading) of the spools supported by the self-expanding spindles, and also a widening of the structure of the moving arms.
Another drawback of such conventional solutions consists in that they have considerable costs of provision owing to the high number of components that constitute them, and such components also require high-precision mechanical machining, together with the need to be made from steel.